The invention relates to a motor vehicle brake system. In particular, the invention relates to the generation of pressure in a hydraulic motor vehicle brake system.
In motor vehicles that are equipped with hydraulic brake systems, hydraulic pumps are used to build up a hydraulic brake pressure independently of the driver. Usually in such cases a drive, for example an electric motor, actuates a plurality of pump elements of a pump that are assigned to differing brake circuits of the motor vehicle. Determination of a defect at one of the pump elements is not difficult, provided that only one pump element is used for each brake circuit. If one of the pump elements is lacking in capacity because of a defect, no further brake pressure whatsoever can be built up in the assigned brake circuit independently of the driver, and the effects of the defect are immediately evident through a failure of the respective brake circuit.
Advanced brake systems require hydraulic pumps that are particularly powerful and whose hydraulic pressure has a more constant characteristic than would be achievable with a single pump element per brake circuit. Therefore pumps that have two or more pump elements per brake circuit are already being used.
If one of the pump elements in such a 4-piston or 6-piston hydraulic pump is lacking in capacity, for example because of a leakage, because of worn components of the pump element or because of another defect, a lack of capacity of the pump as a whole might perhaps become apparent only when a high pressure has to be generated over a relatively long period of time. Travel states of the motor vehicle in which such demands are made on the hydraulic pump include, for example, braking operations in case of hazard. In order to prevent a situation in which a lack of capacity of the hydraulic pump becomes evident only through a lack of effectiveness of the brake system of the motor vehicle during such a vehicle state, it is necessary to check the capacity of the individual pump elements that build up the brake pressure.
Hydraulic pressure sensors, in particular those of high quality that are required for high-grade brake systems, are cost intensive and increase the number of safety-relevant components in the brake system (and, consequently, potentially the probability of a defect). The invention is therefore based on the feature of providing a method by means of which a capacity of pump elements of a pump can also be determined without pressure sensors if necessary (e.g. in the case of saving or failure of the pressure sensor).